Laminated glassine paper coil form



w. A. FoLL ETAL- 3,267,968

LAMI NATED GLAS S I NE PAPER y COIL FOAM Aug. 23, 1966'N Filed March 19. 1963 "Hl y FIG- Nl,

INVENTORS v WILLIAM A. POLL Y ALBIN M. HANCIK 3,267,968 Ice Patented August 23 1966 3,267,968 A LAMINATED GLASSINE PAPER COIL FRM William A. Foll, 3475 Doris Road, Cleveland 9, Ohio, and Albin M. Hancik, 2021 Clarence Ave., Lakewood, Ohio Filed Mar. 19, 1963, Ser. No. 266,345 4 Claims. (Cl. 13S- 141) This invention relates generally as indicated toa speaker coil form and more particularly to the manufacture of a small, dimensionally stable, highly water resistant cylindrical form on which speaker coils may readily be wound.

Most high quality speakers today use aluminum or other metal foil approximately on the order of .0005-.001 inch thick as the form upon which the wires of the speaker coil are wound. However, due to the forms conductive nature, it must be longitudinally slit. Moreover, the foil requires precise dies to make and special adhesives are required to secure the wires to the form and the form to the diaphragm cone. Although aluminum foil is chosen for its lightness of weight, it is still much heavier than desirable and, of course, requires stronger currents than a lighter coil form.

` Since the air gap tolerances in a speaker must be very closely maintained to assure proper performance both in timber and tonal quality, it is necessary to maintain the diameter tolerance of the coil form to .001 inch. Due to the necessary longitudinal slit in the aluminum foil coil form, the speaker coil cannot be wound with the coil form on an expansible mandrel. Instead, the coil must be hand wound and this, of course, greatly increases the cost of speakers.

Aluminum foil is chosen as speaker coil forms because of its water resistant nature. High humidity will cause conventional paper completely cylindrical coil forms to pucker or expand and when dried, to shrink. Thus the required diameter tolerance cannot be maintained and the air gap tolerance will likewise not be maintained affecting the performance of the speaker. It is, of course, well known that the clearances between the voice coil assembly and the pole pieces of the magnet are purposely made quite small in the design of the speaker in that this provides a desirable concentration of magnetic flux in the separating gap wherein the voice coil is mounted. However, a slight variation in the diameter of the voice coil form will destroy this gap tolerance.

It is accordingly a principal object of the present invention to provide a speaker coil form 1/2 to 1/s the weight of more conventional aluminum foil forms.

Another main object is the provision of such a voice coil form which will maintain a diameter tolerance of .001 inch.

Still another object is the provision of aspeaker voice coil form which is highly water resistant.

A further object is the provision of a speaker voice coil form which can inexpensively be manufactured and, moreover, which can be employed with expansible mandrels for the automatic winding of the voice coil thereon.

A yet further object is the provision of an inexpensive voice coil form which will not have any of the inherent disadvantages of aluminum foil coil forms and yet which will produce a speaker having t-he proper high quali-ty characteristics and a longer life.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail a certain illustrative embodiment of ythe invention, this being indicative, however, of

but one of the various ways in which the principle of the invention may be employed.

In said annexed drawing: v i

FIG. 1 is a schematic elevation illustrating a thermosetting coating material being applied to one side of a paper strip;

FIG. 2 is a similar schematic illustration showing the lamination of a polyethylene layer to the opposite side of the same paper strip;

FIG. 3 is a schematic illustration showing the employ ment of the Ithus produced material in conventional tube winding apparatus to form a spiral wound paper tube;

FIG. 4 is a greatly enlarged fragmentary transverse section of the paper tube thus formed; and

FIG. 5 is a fragmentary vertical section of a speaker illustrating the paper tube employed as a voice coil form.

Referring now more particularly to such drawing and especially to FIGS. l and 2, there is illustrated in FIG. 1 a strip of glassine paper 1, which is a thin transparent or translucent paper made usually from digested pulp, such as sulphite pulp, by long continued beating and supercalendering. Such glassine paper can be held quite closely to thickness tolerances and in the illustrated embodiment, the thickness of the initial glassine strip is .001 inch. The top surface of the strip of glassine has applied thereto in liquid form a thermo-curing resin which will penetrate and seal the pores in the glassine paper strip. Such resin may be contained in a hopper 2 to pass through nozzles 3 onto the top surface of the glassine strip and a doctor blade 4 cooperating with a back up roll 5 may be employed to remove excess resin. As the glassine strip moves to the right as seen in FIG. l from beneath the doctor blade 4, the top surface thereof will now be provided with a coating 61 of uncured thermo-setting resin which will penetrate the pores and which will not appreciably affect the .001 thickness of the glassine paper strip. The coated strip then moves into a tunnel evaporator and lheater unit 7 which will raise the temperature of the glassine strip and the resin thereon to approximately 200 F. Although the tunnel evaporator and drier 7 will not completely cure the applied coating 6, it will drive off solvents in the resin and remove the tackiness thereof so that the now coated strip of glassinemay be wound in coil form as indicated at 8 for storage and transportation purposes.

The glassine paper strip 1 is thus treated on one side only with a sealant or penetrant of a thermo-curing nature which will enter the pores of the glassine and be thoroughly bonded thereto when set. The application of such sealant to the glassine renders one side thereof highly water resistant. As such thermocuring resin, it is preferred to use an epichlorohydrin-bisphenol condensate, commonly known as an epoxy resin. Although epoxy resins are preferred, other thermosetting resins may also be employed such as polyesters, phenol-formaldehydes, phenol-furfurals and urea formaldehydes. As a preferred epoxy sealant, Bostik 7008, manufactured by BB Chemical Company of Cambridge, Massachusetts, may be employed. Such thermosetting, synthetic resin contains a solvent which will be driven from the sealant in the tunnel evaporater 7 prior to the coated strip being wound in the coil 8. The time required for the sealant properly to cure is, of course, dependent upon the temperature and such sealant will cure at room temperature over a relatively long period of time. In any event, before the next step in the described process, the .sealant must be cured sufficiently to prevent the same from softening or becoming tacky upon a further application of heat.

After approximately no less than 24 hours, the now coated glassine strip is fed through a polyethylene extruder shown schematically at 10 in FIG. 2. The poly ethylene which may be supplied from a hopper or screw extruder 11 is heated to approximately 600 F. when it contacts the glassine strip 1 and the ltemperature of the polyethylene will further set the epoxy coating 6 which is now on the opposite side of the glassine strip 1. When polyethylene is heated to such a temperature, it will immediately bond with the uncoated side of the glassine strip 1 and is in a tacky condition. The lamination of polyethylene and coated glassine paper is then passed through top and lbottom chill rolls 12 and 13, respectively, which will cool the layer of polyethylene thereon to eliminate tackiness so that the material can now be coiled in coil form as indicated at 14 for storage and shipment. It will, of course, be understood that the coating 6 on the bottom side of `the glassine strip 1 in FIG. 2 must be suliciently heat-cured so that it will not soften or otherwise be affected by the 600 F. temperature of the applied polyethylene on the opposite side of the strip. The thickness of the lamination of polyethylene on the glassine paper strip will be held to .0005 inch by application of approximately 7 pounds of polyethylene per ream of paper.

There is then produced in the coil 14 a material which comprises a strip of glassine paper 1 having a coating of thermo-cured epoxy resin 6 on one side and a lamination or layer of polyethylene 15 on the other side. Since the layer of polyethylene is .0005 inch thick, the total thickness of the material will be ,0015 inch. The material is now slit into tapes approximately 1% to l1/2 inches wide for tube winding.

Referring now to FIG. 3, there is illustrated a substantially conventional tube winding apparatus which comprises a smooth mandrel 17 about which two plies of the same thickness of such material 18 and 19 are spirally wrapped and lapped to form a two ply tube of such material. Such plies will be fed to the mandrel at a predetermined lead angle from spools of such tape. The plies will be drawn from the storage rolls by a winding belt (not shown) to form a spirally wound -tube shown generally at 20. Such tube will move longitudinally off the mandrel to be severed by a rotating flying knife 21 into short segment cylindrical forms shown at 22. In conventional paper tube winding, adhesives are employed to hold the lapped plies Vtogether but in the present invention, the lamination of polyethylene on one side of the plies 18 and 19 will be employed to adhere the plies together to form an integrated two ply paper tube. The lead angle at which the plies are disposed with respect to the axis Iof the mandrel 17 may vary from 30 to 60 and such lead angle will be a factor in determining the speed at which the wound tube extends from the end of the mandrel 17. The ply 18, which is the rst Wound ply, will have the layer of polyethylene 15 on the exterior thereof as it is wound about the mandrel. Conversely, the ply 19 will have the layer of polyethylene 15 thereon interiorly as it is wound about the mandrel. The ply 19 thus overlaps the ply 18 and is the outer ply of the two ply paper tube thus formed.

In order to cause the respective layers Iof polyethylene 15 -on the exterior and interior of the plies 18 and 19, respectively, to bond or fuse together as the tube is wound, heating elements 24 and 25 which may be of the electrical type are positioned closely adjacent and yet spaced from the plies 18 and 19 on the side which carries the polyethylene. The distance between the heating elements and the plies will be closely controlled and to some degree, such spacing will be dependent upon the speed at which the tube is wound. The heating elements then soften the polyethylene to the point wherein the two layers of such polyethylene on the respective plies will then-fuse into a single intermediate layer, shown at 27 in FIG. 4,not only firmly adhering the two plies together, but providing an intermediate layer in the tube thus formed of polyethylene which will make the vtube water impervious. As the tube is wound, the tension on the winding belt and plies 18 and 19 will supply the required bonding pressure and when the polyethylene cools, the

fusion has taken place rmly to secure the plies of the tube together. The tube is then severed into appropriate lengths for use as coil forms for speaker coils. It will be noted, that in order to maintain the inside and -outside diameter tolerances of the tube, a butt joint providing a very minor gap between adjacent turns of the plies as indicated at 28 is utilized in order to avoid any lapping of the ply material. The inside ply will then be provided with a spiral gap seam which will be closed by the polyethylene. Similarly, the outside ply is provided with a spiral gap seam which will be axially oifset from the seam in the inside ply as indicated at 29.

There is now produced, as seen in FIG. 4, a short length cylindrical tube which may have a peripheral wall thickness of .003 inch. Reading from top to bottom or outside to` inside as seen in FIG. 4, the tube wall is cornprised of an external coating of epoxide resin 30 which has been heat-cured to provide a highly water resistant exterior coating. Such epoxide resin is penetrated into the pores of the glassine paper strip 31 which has interiorly bonded thereto a .0005 inch lamination of polyethylene which is now fused to the similar lamination of polyethylene on the ply 18 to form an intermediate lamination 32 within the tube which is now .001 inch thick. The intermediate lamination 32 is thus comprised of the .0005 inch thick laminate on both the exterior and interior plies. The interior glassine paper 33 has interiorly bonded thereto an epoxy `coating 34 which may be identical in form to the coating 30. Such epoxy coatings prevent humidity penetration and thus puckering of the glassine to maintain the proper dimensional thickness of the tuibe. The epoxy coatings may contain a dye since they are normally colorless. This then provides a visual indication that the coating has been applied and color coding is also then possible.

It is, of course, necessary that the epoxy coatings 30 and 34 for the tube be previously cured so that they will not soften or otherwise change in stability as the tapes pass adjacent the heating elements 24 and 25 heating the polyethylene laminate thereon to .fusing temperature.

The short length tube 22 is then placed upon an expansi'ble mandrel and may automatically be wound with a very small diameter wire such as .001 to .0005 inch to form the voice coil. The wire normally passes through an alcohol bath to soften the Varnish or other insulation on the wire so that it will stick to the coil form. The wires are necessarily wound quite tight and may even indent the exterior surface of the coil form. Here again is a further advantage of the present coil form over aluminum foil forms in that the indentation of the exterior surface of the present coil form will facilitate the securance of the wires to the form.

In FIG. 5 there is illustrated somewhat schematically a P-M dynamic loudspeaker showing the coil form of the present invention in place. The voice coil 36 wound thereon surrounds a center pole piece 37 of a permanent magnet. The outer end Iof the form 22 is adhesively secured to the .apex of the .speaker cone diaphragm 38 and a spider or voice coil support 39 is also secured thereto. The permanent magnet will induce a magnetic flux, the path of which is shown by the arrows 40 and 41. The air gap 42 around the outside of the voice coil 36 is intentionally maintained as small as possible and it 'can readily be seen that any variation in the diameter or any puckering of the coil form my close .such gap and cause a malfunction or poor performance of the speaker. The outer edge of the cone diaphragm 38 is supported on a spider 43 in conventional manner.

It can now be seen that there is provided a speaker voice coil form which will provide the dimensional stability under adverse temperature and humidity conditions heretofore thought available only with metal foils such as aluminum. Moreover, the present coil form is lighter in weight and does not require the longitudinal slit for insulation purposes. Such slit in aluminum foil coil forms often collects dust and even the most minute dust particle in such slit can impair the operation of the speaker. Furthermore, aluminum foil coil forms require very special and expensive tools to produce and must be heated to drive oi oils therein which would otherwise preclude the varnish on the wire or other adhesive from adhering thereto. Finally, and perhaps most importantly, the dimensional stability of the coil form of the present invention permits the coil to be machine wound on an expansible mandrel rather than h-and wound as was iheretofore the case in high quality speakers especially of the smaller variety such as tweeters. In any event, a more economical, higher quality and longer life speaker is thus aorded.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. A speaker voice coil form comprising an outer ply of glassine paper, an external coating of thermosetting resin thereon, an internal ply of glassine paper, an inner layer of heat sealable polyethylene on said outer ply of glassine paper bonded to an outer layer of heat sealable polyethylene on said internal ply of glassine paper, and a coating of thermosetting resin on the interior of said coil form on the inner ply of glass-ine paper.

2. The method of making a speaker voice coil form and like tubular products comprising the steps of applying a thermosetting resin sealant to one side of a glassine paper strip, heat-curing said thermosetting resin, laminating a heat sealable polyethylene to the opposite side of such strip, spirally Winding two plies of such strip material with the heat sealable polyethylene therebetween, heating 3 such polyethylene to bond such plies together, and cutting the thus formed spirally wound tube to form the speaker voice coil form. p

3. The method of makinga speaker voice coil comprising the .steps of yapplying a thermosetting resin to one side of a glassine paper strip, heat-curing such resin, applying a layer of heat sealable polyethylene to the opposite side of such strip, spirally winding two plies of such strip on a mandrel with the heat sealable polyethylene therebetween to form a .spirally wound glassine paper tube, heating such polyethylene to bond such plies together, and severing such tube to form a short length coil form.

4. The method set forth in claim 3 including the step of mounting said form on an expansible mandrel and winding a wire coil on said form.

References Cited by the Examiner LEWIS H. MYERS, Primary Examiner.

5 JOHN F. BURNS, ROBERT K. SCHAEFER, 

1. A SPEAKER VOICE COIL FORM COMPRISING AN OUTER PLY OF GLASSINE PAPER, AN EXTERNAL COATING OF THERMOSETTING RESIN THEREON, AN INTERNAL PLY OF GLASSINE PAPER, AN INNER LAYER OF HEAT SEALABLE POLYETHLENE ON SAID OUTER PLY OF GLASSINE PAPER BONDED TO AN OUTER LAYER OF HEAT SEALABLE POLYETHYLENE ON SAID INTERNAL PLY OF GLASSINE PAPER, AND A COATING OF THERMOSETTING RESIN ON THE INTERIOR OF SAID COIL FORM ON THE INNER PLY OF GLASSINE PAPER. 